summaryrefslogtreecommitdiff
path: root/net/sunrpc/auth_gss/gss_krb5_crypto.c
blob: 634b6c6e0dcbc9016cc3f8f03bd8fa39c4ca7667 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
/*
 *  linux/net/sunrpc/gss_krb5_crypto.c
 *
 *  Copyright (c) 2000-2008 The Regents of the University of Michigan.
 *  All rights reserved.
 *
 *  Andy Adamson   <andros@umich.edu>
 *  Bruce Fields   <bfields@umich.edu>
 */

/*
 * Copyright (C) 1998 by the FundsXpress, INC.
 *
 * All rights reserved.
 *
 * Export of this software from the United States of America may require
 * a specific license from the United States Government.  It is the
 * responsibility of any person or organization contemplating export to
 * obtain such a license before exporting.
 *
 * WITHIN THAT CONSTRAINT, permission to use, copy, modify, and
 * distribute this software and its documentation for any purpose and
 * without fee is hereby granted, provided that the above copyright
 * notice appear in all copies and that both that copyright notice and
 * this permission notice appear in supporting documentation, and that
 * the name of FundsXpress. not be used in advertising or publicity pertaining
 * to distribution of the software without specific, written prior
 * permission.  FundsXpress makes no representations about the suitability of
 * this software for any purpose.  It is provided "as is" without express
 * or implied warranty.
 *
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
 * WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
 */

#include <crypto/algapi.h>
#include <crypto/hash.h>
#include <crypto/skcipher.h>
#include <linux/err.h>
#include <linux/types.h>
#include <linux/mm.h>
#include <linux/scatterlist.h>
#include <linux/highmem.h>
#include <linux/pagemap.h>
#include <linux/random.h>
#include <linux/sunrpc/gss_krb5.h>
#include <linux/sunrpc/xdr.h>

#if IS_ENABLED(CONFIG_SUNRPC_DEBUG)
# define RPCDBG_FACILITY        RPCDBG_AUTH
#endif

u32
krb5_encrypt(
	struct crypto_sync_skcipher *tfm,
	void * iv,
	void * in,
	void * out,
	int length)
{
	u32 ret = -EINVAL;
	struct scatterlist sg[1];
	u8 local_iv[GSS_KRB5_MAX_BLOCKSIZE] = {0};
	SYNC_SKCIPHER_REQUEST_ON_STACK(req, tfm);

	if (length % crypto_sync_skcipher_blocksize(tfm) != 0)
		goto out;

	if (crypto_sync_skcipher_ivsize(tfm) > GSS_KRB5_MAX_BLOCKSIZE) {
		dprintk("RPC:       gss_k5encrypt: tfm iv size too large %d\n",
			crypto_sync_skcipher_ivsize(tfm));
		goto out;
	}

	if (iv)
		memcpy(local_iv, iv, crypto_sync_skcipher_ivsize(tfm));

	memcpy(out, in, length);
	sg_init_one(sg, out, length);

	skcipher_request_set_sync_tfm(req, tfm);
	skcipher_request_set_callback(req, 0, NULL, NULL);
	skcipher_request_set_crypt(req, sg, sg, length, local_iv);

	ret = crypto_skcipher_encrypt(req);
	skcipher_request_zero(req);
out:
	dprintk("RPC:       krb5_encrypt returns %d\n", ret);
	return ret;
}

u32
krb5_decrypt(
     struct crypto_sync_skcipher *tfm,
     void * iv,
     void * in,
     void * out,
     int length)
{
	u32 ret = -EINVAL;
	struct scatterlist sg[1];
	u8 local_iv[GSS_KRB5_MAX_BLOCKSIZE] = {0};
	SYNC_SKCIPHER_REQUEST_ON_STACK(req, tfm);

	if (length % crypto_sync_skcipher_blocksize(tfm) != 0)
		goto out;

	if (crypto_sync_skcipher_ivsize(tfm) > GSS_KRB5_MAX_BLOCKSIZE) {
		dprintk("RPC:       gss_k5decrypt: tfm iv size too large %d\n",
			crypto_sync_skcipher_ivsize(tfm));
		goto out;
	}
	if (iv)
		memcpy(local_iv, iv, crypto_sync_skcipher_ivsize(tfm));

	memcpy(out, in, length);
	sg_init_one(sg, out, length);

	skcipher_request_set_sync_tfm(req, tfm);
	skcipher_request_set_callback(req, 0, NULL, NULL);
	skcipher_request_set_crypt(req, sg, sg, length, local_iv);

	ret = crypto_skcipher_decrypt(req);
	skcipher_request_zero(req);
out:
	dprintk("RPC:       gss_k5decrypt returns %d\n",ret);
	return ret;
}

static int
checksummer(struct scatterlist *sg, void *data)
{
	struct ahash_request *req = data;

	ahash_request_set_crypt(req, sg, NULL, sg->length);

	return crypto_ahash_update(req);
}

/*
 * checksum the plaintext data and hdrlen bytes of the token header
 * The checksum is performed over the first 8 bytes of the
 * gss token header and then over the data body
 */
u32
make_checksum(struct krb5_ctx *kctx, char *header, int hdrlen,
	      struct xdr_buf *body, int body_offset, u8 *cksumkey,
	      unsigned int usage, struct xdr_netobj *cksumout)
{
	struct crypto_ahash *tfm;
	struct ahash_request *req;
	struct scatterlist              sg[1];
	int err = -1;
	u8 *checksumdata;
	unsigned int checksumlen;

	if (cksumout->len < kctx->gk5e->cksumlength) {
		dprintk("%s: checksum buffer length, %u, too small for %s\n",
			__func__, cksumout->len, kctx->gk5e->name);
		return GSS_S_FAILURE;
	}

	checksumdata = kmalloc(GSS_KRB5_MAX_CKSUM_LEN, GFP_NOFS);
	if (checksumdata == NULL)
		return GSS_S_FAILURE;

	tfm = crypto_alloc_ahash(kctx->gk5e->cksum_name, 0, CRYPTO_ALG_ASYNC);
	if (IS_ERR(tfm))
		goto out_free_cksum;

	req = ahash_request_alloc(tfm, GFP_NOFS);
	if (!req)
		goto out_free_ahash;

	ahash_request_set_callback(req, CRYPTO_TFM_REQ_MAY_SLEEP, NULL, NULL);

	checksumlen = crypto_ahash_digestsize(tfm);

	if (cksumkey != NULL) {
		err = crypto_ahash_setkey(tfm, cksumkey,
					  kctx->gk5e->keylength);
		if (err)
			goto out;
	}

	err = crypto_ahash_init(req);
	if (err)
		goto out;
	sg_init_one(sg, header, hdrlen);
	ahash_request_set_crypt(req, sg, NULL, hdrlen);
	err = crypto_ahash_update(req);
	if (err)
		goto out;
	err = xdr_process_buf(body, body_offset, body->len - body_offset,
			      checksummer, req);
	if (err)
		goto out;
	ahash_request_set_crypt(req, NULL, checksumdata, 0);
	err = crypto_ahash_final(req);
	if (err)
		goto out;

	switch (kctx->gk5e->ctype) {
	case CKSUMTYPE_RSA_MD5:
		err = kctx->gk5e->encrypt(kctx->seq, NULL, checksumdata,
					  checksumdata, checksumlen);
		if (err)
			goto out;
		memcpy(cksumout->data,
		       checksumdata + checksumlen - kctx->gk5e->cksumlength,
		       kctx->gk5e->cksumlength);
		break;
	case CKSUMTYPE_HMAC_SHA1_DES3:
		memcpy(cksumout->data, checksumdata, kctx->gk5e->cksumlength);
		break;
	default:
		BUG();
		break;
	}
	cksumout->len = kctx->gk5e->cksumlength;
out:
	ahash_request_free(req);
out_free_ahash:
	crypto_free_ahash(tfm);
out_free_cksum:
	kfree(checksumdata);
	return err ? GSS_S_FAILURE : 0;
}

/*
 * checksum the plaintext data and hdrlen bytes of the token header
 * Per rfc4121, sec. 4.2.4, the checksum is performed over the data
 * body then over the first 16 octets of the MIC token
 * Inclusion of the header data in the calculation of the
 * checksum is optional.
 */
u32
make_checksum_v2(struct krb5_ctx *kctx, char *header, int hdrlen,
		 struct xdr_buf *body, int body_offset, u8 *cksumkey,
		 unsigned int usage, struct xdr_netobj *cksumout)
{
	struct crypto_ahash *tfm;
	struct ahash_request *req;
	struct scatterlist sg[1];
	int err = -1;
	u8 *checksumdata;

	if (kctx->gk5e->keyed_cksum == 0) {
		dprintk("%s: expected keyed hash for %s\n",
			__func__, kctx->gk5e->name);
		return GSS_S_FAILURE;
	}
	if (cksumkey == NULL) {
		dprintk("%s: no key supplied for %s\n",
			__func__, kctx->gk5e->name);
		return GSS_S_FAILURE;
	}

	checksumdata = kmalloc(GSS_KRB5_MAX_CKSUM_LEN, GFP_NOFS);
	if (!checksumdata)
		return GSS_S_FAILURE;

	tfm = crypto_alloc_ahash(kctx->gk5e->cksum_name, 0, CRYPTO_ALG_ASYNC);
	if (IS_ERR(tfm))
		goto out_free_cksum;

	req = ahash_request_alloc(tfm, GFP_NOFS);
	if (!req)
		goto out_free_ahash;

	ahash_request_set_callback(req, CRYPTO_TFM_REQ_MAY_SLEEP, NULL, NULL);

	err = crypto_ahash_setkey(tfm, cksumkey, kctx->gk5e->keylength);
	if (err)
		goto out;

	err = crypto_ahash_init(req);
	if (err)
		goto out;
	err = xdr_process_buf(body, body_offset, body->len - body_offset,
			      checksummer, req);
	if (err)
		goto out;
	if (header != NULL) {
		sg_init_one(sg, header, hdrlen);
		ahash_request_set_crypt(req, sg, NULL, hdrlen);
		err = crypto_ahash_update(req);
		if (err)
			goto out;
	}
	ahash_request_set_crypt(req, NULL, checksumdata, 0);
	err = crypto_ahash_final(req);
	if (err)
		goto out;

	cksumout->len = kctx->gk5e->cksumlength;

	switch (kctx->gk5e->ctype) {
	case CKSUMTYPE_HMAC_SHA1_96_AES128:
	case CKSUMTYPE_HMAC_SHA1_96_AES256:
		/* note that this truncates the hash */
		memcpy(cksumout->data, checksumdata, kctx->gk5e->cksumlength);
		break;
	default:
		BUG();
		break;
	}
out:
	ahash_request_free(req);
out_free_ahash:
	crypto_free_ahash(tfm);
out_free_cksum:
	kfree(checksumdata);
	return err ? GSS_S_FAILURE : 0;
}

struct encryptor_desc {
	u8 iv[GSS_KRB5_MAX_BLOCKSIZE];
	struct skcipher_request *req;
	int pos;
	struct xdr_buf *outbuf;
	struct page **pages;
	struct scatterlist infrags[4];
	struct scatterlist outfrags[4];
	int fragno;
	int fraglen;
};

static int
encryptor(struct scatterlist *sg, void *data)
{
	struct encryptor_desc *desc = data;
	struct xdr_buf *outbuf = desc->outbuf;
	struct crypto_sync_skcipher *tfm =
		crypto_sync_skcipher_reqtfm(desc->req);
	struct page *in_page;
	int thislen = desc->fraglen + sg->length;
	int fraglen, ret;
	int page_pos;

	/* Worst case is 4 fragments: head, end of page 1, start
	 * of page 2, tail.  Anything more is a bug. */
	BUG_ON(desc->fragno > 3);

	page_pos = desc->pos - outbuf->head[0].iov_len;
	if (page_pos >= 0 && page_pos < outbuf->page_len) {
		/* pages are not in place: */
		int i = (page_pos + outbuf->page_base) >> PAGE_SHIFT;
		in_page = desc->pages[i];
	} else {
		in_page = sg_page(sg);
	}
	sg_set_page(&desc->infrags[desc->fragno], in_page, sg->length,
		    sg->offset);
	sg_set_page(&desc->outfrags[desc->fragno], sg_page(sg), sg->length,
		    sg->offset);
	desc->fragno++;
	desc->fraglen += sg->length;
	desc->pos += sg->length;

	fraglen = thislen & (crypto_sync_skcipher_blocksize(tfm) - 1);
	thislen -= fraglen;

	if (thislen == 0)
		return 0;

	sg_mark_end(&desc->infrags[desc->fragno - 1]);
	sg_mark_end(&desc->outfrags[desc->fragno - 1]);

	skcipher_request_set_crypt(desc->req, desc->infrags, desc->outfrags,
				   thislen, desc->iv);

	ret = crypto_skcipher_encrypt(desc->req);
	if (ret)
		return ret;

	sg_init_table(desc->infrags, 4);
	sg_init_table(desc->outfrags, 4);

	if (fraglen) {
		sg_set_page(&desc->outfrags[0], sg_page(sg), fraglen,
				sg->offset + sg->length - fraglen);
		desc->infrags[0] = desc->outfrags[0];
		sg_assign_page(&desc->infrags[0], in_page);
		desc->fragno = 1;
		desc->fraglen = fraglen;
	} else {
		desc->fragno = 0;
		desc->fraglen = 0;
	}
	return 0;
}

int
gss_encrypt_xdr_buf(struct crypto_sync_skcipher *tfm, struct xdr_buf *buf,
		    int offset, struct page **pages)
{
	int ret;
	struct encryptor_desc desc;
	SYNC_SKCIPHER_REQUEST_ON_STACK(req, tfm);

	BUG_ON((buf->len - offset) % crypto_sync_skcipher_blocksize(tfm) != 0);

	skcipher_request_set_sync_tfm(req, tfm);
	skcipher_request_set_callback(req, 0, NULL, NULL);

	memset(desc.iv, 0, sizeof(desc.iv));
	desc.req = req;
	desc.pos = offset;
	desc.outbuf = buf;
	desc.pages = pages;
	desc.fragno = 0;
	desc.fraglen = 0;

	sg_init_table(desc.infrags, 4);
	sg_init_table(desc.outfrags, 4);

	ret = xdr_process_buf(buf, offset, buf->len - offset, encryptor, &desc);
	skcipher_request_zero(req);
	return ret;
}

struct decryptor_desc {
	u8 iv[GSS_KRB5_MAX_BLOCKSIZE];
	struct skcipher_request *req;
	struct scatterlist frags[4];
	int fragno;
	int fraglen;
};

static int
decryptor(struct scatterlist *sg, void *data)
{
	struct decryptor_desc *desc = data;
	int thislen = desc->fraglen + sg->length;
	struct crypto_sync_skcipher *tfm =
		crypto_sync_skcipher_reqtfm(desc->req);
	int fraglen, ret;

	/* Worst case is 4 fragments: head, end of page 1, start
	 * of page 2, tail.  Anything more is a bug. */
	BUG_ON(desc->fragno > 3);
	sg_set_page(&desc->frags[desc->fragno], sg_page(sg), sg->length,
		    sg->offset);
	desc->fragno++;
	desc->fraglen += sg->length;

	fraglen = thislen & (crypto_sync_skcipher_blocksize(tfm) - 1);
	thislen -= fraglen;

	if (thislen == 0)
		return 0;

	sg_mark_end(&desc->frags[desc->fragno - 1]);

	skcipher_request_set_crypt(desc->req, desc->frags, desc->frags,
				   thislen, desc->iv);

	ret = crypto_skcipher_decrypt(desc->req);
	if (ret)
		return ret;

	sg_init_table(desc->frags, 4);

	if (fraglen) {
		sg_set_page(&desc->frags[0], sg_page(sg), fraglen,
				sg->offset + sg->length - fraglen);
		desc->fragno = 1;
		desc->fraglen = fraglen;
	} else {
		desc->fragno = 0;
		desc->fraglen = 0;
	}
	return 0;
}

int
gss_decrypt_xdr_buf(struct crypto_sync_skcipher *tfm, struct xdr_buf *buf,
		    int offset)
{
	int ret;
	struct decryptor_desc desc;
	SYNC_SKCIPHER_REQUEST_ON_STACK(req, tfm);

	/* XXXJBF: */
	BUG_ON((buf->len - offset) % crypto_sync_skcipher_blocksize(tfm) != 0);

	skcipher_request_set_sync_tfm(req, tfm);
	skcipher_request_set_callback(req, 0, NULL, NULL);

	memset(desc.iv, 0, sizeof(desc.iv));
	desc.req = req;
	desc.fragno = 0;
	desc.fraglen = 0;

	sg_init_table(desc.frags, 4);

	ret = xdr_process_buf(buf, offset, buf->len - offset, decryptor, &desc);
	skcipher_request_zero(req);
	return ret;
}

/*
 * This function makes the assumption that it was ultimately called
 * from gss_wrap().
 *
 * The client auth_gss code moves any existing tail data into a
 * separate page before calling gss_wrap.
 * The server svcauth_gss code ensures that both the head and the
 * tail have slack space of RPC_MAX_AUTH_SIZE before calling gss_wrap.
 *
 * Even with that guarantee, this function may be called more than
 * once in the processing of gss_wrap().  The best we can do is
 * verify at compile-time (see GSS_KRB5_SLACK_CHECK) that the
 * largest expected shift will fit within RPC_MAX_AUTH_SIZE.
 * At run-time we can verify that a single invocation of this
 * function doesn't attempt to use more the RPC_MAX_AUTH_SIZE.
 */

int
xdr_extend_head(struct xdr_buf *buf, unsigned int base, unsigned int shiftlen)
{
	u8 *p;

	if (shiftlen == 0)
		return 0;

	BUILD_BUG_ON(GSS_KRB5_MAX_SLACK_NEEDED > RPC_MAX_AUTH_SIZE);
	BUG_ON(shiftlen > RPC_MAX_AUTH_SIZE);

	p = buf->head[0].iov_base + base;

	memmove(p + shiftlen, p, buf->head[0].iov_len - base);

	buf->head[0].iov_len += shiftlen;
	buf->len += shiftlen;

	return 0;
}

static u32
gss_krb5_cts_crypt(struct crypto_sync_skcipher *cipher, struct xdr_buf *buf,
		   u32 offset, u8 *iv, struct page **pages, int encrypt)
{
	u32 ret;
	struct scatterlist sg[1];
	SYNC_SKCIPHER_REQUEST_ON_STACK(req, cipher);
	u8 *data;
	struct page **save_pages;
	u32 len = buf->len - offset;

	if (len > GSS_KRB5_MAX_BLOCKSIZE * 2) {
		WARN_ON(0);
		return -ENOMEM;
	}
	data = kmalloc(GSS_KRB5_MAX_BLOCKSIZE * 2, GFP_NOFS);
	if (!data)
		return -ENOMEM;

	/*
	 * For encryption, we want to read from the cleartext
	 * page cache pages, and write the encrypted data to
	 * the supplied xdr_buf pages.
	 */
	save_pages = buf->pages;
	if (encrypt)
		buf->pages = pages;

	ret = read_bytes_from_xdr_buf(buf, offset, data, len);
	buf->pages = save_pages;
	if (ret)
		goto out;

	sg_init_one(sg, data, len);

	skcipher_request_set_sync_tfm(req, cipher);
	skcipher_request_set_callback(req, 0, NULL, NULL);
	skcipher_request_set_crypt(req, sg, sg, len, iv);

	if (encrypt)
		ret = crypto_skcipher_encrypt(req);
	else
		ret = crypto_skcipher_decrypt(req);

	skcipher_request_zero(req);

	if (ret)
		goto out;

	ret = write_bytes_to_xdr_buf(buf, offset, data, len);

out:
	kfree(data);
	return ret;
}

u32
gss_krb5_aes_encrypt(struct krb5_ctx *kctx, u32 offset,
		     struct xdr_buf *buf, struct page **pages)
{
	u32 err;
	struct xdr_netobj hmac;
	u8 *cksumkey;
	u8 *ecptr;
	struct crypto_sync_skcipher *cipher, *aux_cipher;
	int blocksize;
	struct page **save_pages;
	int nblocks, nbytes;
	struct encryptor_desc desc;
	u32 cbcbytes;
	unsigned int usage;

	if (kctx->initiate) {
		cipher = kctx->initiator_enc;
		aux_cipher = kctx->initiator_enc_aux;
		cksumkey = kctx->initiator_integ;
		usage = KG_USAGE_INITIATOR_SEAL;
	} else {
		cipher = kctx->acceptor_enc;
		aux_cipher = kctx->acceptor_enc_aux;
		cksumkey = kctx->acceptor_integ;
		usage = KG_USAGE_ACCEPTOR_SEAL;
	}
	blocksize = crypto_sync_skcipher_blocksize(cipher);

	/* hide the gss token header and insert the confounder */
	offset += GSS_KRB5_TOK_HDR_LEN;
	if (xdr_extend_head(buf, offset, kctx->gk5e->conflen))
		return GSS_S_FAILURE;
	gss_krb5_make_confounder(buf->head[0].iov_base + offset, kctx->gk5e->conflen);
	offset -= GSS_KRB5_TOK_HDR_LEN;

	if (buf->tail[0].iov_base != NULL) {
		ecptr = buf->tail[0].iov_base + buf->tail[0].iov_len;
	} else {
		buf->tail[0].iov_base = buf->head[0].iov_base
							+ buf->head[0].iov_len;
		buf->tail[0].iov_len = 0;
		ecptr = buf->tail[0].iov_base;
	}

	/* copy plaintext gss token header after filler (if any) */
	memcpy(ecptr, buf->head[0].iov_base + offset, GSS_KRB5_TOK_HDR_LEN);
	buf->tail[0].iov_len += GSS_KRB5_TOK_HDR_LEN;
	buf->len += GSS_KRB5_TOK_HDR_LEN;

	/* Do the HMAC */
	hmac.len = GSS_KRB5_MAX_CKSUM_LEN;
	hmac.data = buf->tail[0].iov_base + buf->tail[0].iov_len;

	/*
	 * When we are called, pages points to the real page cache
	 * data -- which we can't go and encrypt!  buf->pages points
	 * to scratch pages which we are going to send off to the
	 * client/server.  Swap in the plaintext pages to calculate
	 * the hmac.
	 */
	save_pages = buf->pages;
	buf->pages = pages;

	err = make_checksum_v2(kctx, NULL, 0, buf,
			       offset + GSS_KRB5_TOK_HDR_LEN,
			       cksumkey, usage, &hmac);
	buf->pages = save_pages;
	if (err)
		return GSS_S_FAILURE;

	nbytes = buf->len - offset - GSS_KRB5_TOK_HDR_LEN;
	nblocks = (nbytes + blocksize - 1) / blocksize;
	cbcbytes = 0;
	if (nblocks > 2)
		cbcbytes = (nblocks - 2) * blocksize;

	memset(desc.iv, 0, sizeof(desc.iv));

	if (cbcbytes) {
		SYNC_SKCIPHER_REQUEST_ON_STACK(req, aux_cipher);

		desc.pos = offset + GSS_KRB5_TOK_HDR_LEN;
		desc.fragno = 0;
		desc.fraglen = 0;
		desc.pages = pages;
		desc.outbuf = buf;
		desc.req = req;

		skcipher_request_set_sync_tfm(req, aux_cipher);
		skcipher_request_set_callback(req, 0, NULL, NULL);

		sg_init_table(desc.infrags, 4);
		sg_init_table(desc.outfrags, 4);

		err = xdr_process_buf(buf, offset + GSS_KRB5_TOK_HDR_LEN,
				      cbcbytes, encryptor, &desc);
		skcipher_request_zero(req);
		if (err)
			goto out_err;
	}

	/* Make sure IV carries forward from any CBC results. */
	err = gss_krb5_cts_crypt(cipher, buf,
				 offset + GSS_KRB5_TOK_HDR_LEN + cbcbytes,
				 desc.iv, pages, 1);
	if (err) {
		err = GSS_S_FAILURE;
		goto out_err;
	}

	/* Now update buf to account for HMAC */
	buf->tail[0].iov_len += kctx->gk5e->cksumlength;
	buf->len += kctx->gk5e->cksumlength;

out_err:
	if (err)
		err = GSS_S_FAILURE;
	return err;
}

u32
gss_krb5_aes_decrypt(struct krb5_ctx *kctx, u32 offset, u32 len,
		     struct xdr_buf *buf, u32 *headskip, u32 *tailskip)
{
	struct xdr_buf subbuf;
	u32 ret = 0;
	u8 *cksum_key;
	struct crypto_sync_skcipher *cipher, *aux_cipher;
	struct xdr_netobj our_hmac_obj;
	u8 our_hmac[GSS_KRB5_MAX_CKSUM_LEN];
	u8 pkt_hmac[GSS_KRB5_MAX_CKSUM_LEN];
	int nblocks, blocksize, cbcbytes;
	struct decryptor_desc desc;
	unsigned int usage;

	if (kctx->initiate) {
		cipher = kctx->acceptor_enc;
		aux_cipher = kctx->acceptor_enc_aux;
		cksum_key = kctx->acceptor_integ;
		usage = KG_USAGE_ACCEPTOR_SEAL;
	} else {
		cipher = kctx->initiator_enc;
		aux_cipher = kctx->initiator_enc_aux;
		cksum_key = kctx->initiator_integ;
		usage = KG_USAGE_INITIATOR_SEAL;
	}
	blocksize = crypto_sync_skcipher_blocksize(cipher);


	/* create a segment skipping the header and leaving out the checksum */
	xdr_buf_subsegment(buf, &subbuf, offset + GSS_KRB5_TOK_HDR_LEN,
				    (len - offset - GSS_KRB5_TOK_HDR_LEN -
				     kctx->gk5e->cksumlength));

	nblocks = (subbuf.len + blocksize - 1) / blocksize;

	cbcbytes = 0;
	if (nblocks > 2)
		cbcbytes = (nblocks - 2) * blocksize;

	memset(desc.iv, 0, sizeof(desc.iv));

	if (cbcbytes) {
		SYNC_SKCIPHER_REQUEST_ON_STACK(req, aux_cipher);

		desc.fragno = 0;
		desc.fraglen = 0;
		desc.req = req;

		skcipher_request_set_sync_tfm(req, aux_cipher);
		skcipher_request_set_callback(req, 0, NULL, NULL);

		sg_init_table(desc.frags, 4);

		ret = xdr_process_buf(&subbuf, 0, cbcbytes, decryptor, &desc);
		skcipher_request_zero(req);
		if (ret)
			goto out_err;
	}

	/* Make sure IV carries forward from any CBC results. */
	ret = gss_krb5_cts_crypt(cipher, &subbuf, cbcbytes, desc.iv, NULL, 0);
	if (ret)
		goto out_err;


	/* Calculate our hmac over the plaintext data */
	our_hmac_obj.len = sizeof(our_hmac);
	our_hmac_obj.data = our_hmac;

	ret = make_checksum_v2(kctx, NULL, 0, &subbuf, 0,
			       cksum_key, usage, &our_hmac_obj);
	if (ret)
		goto out_err;

	/* Get the packet's hmac value */
	ret = read_bytes_from_xdr_buf(buf, len - kctx->gk5e->cksumlength,
				      pkt_hmac, kctx->gk5e->cksumlength);
	if (ret)
		goto out_err;

	if (crypto_memneq(pkt_hmac, our_hmac, kctx->gk5e->cksumlength) != 0) {
		ret = GSS_S_BAD_SIG;
		goto out_err;
	}
	*headskip = kctx->gk5e->conflen;
	*tailskip = kctx->gk5e->cksumlength;
out_err:
	if (ret && ret != GSS_S_BAD_SIG)
		ret = GSS_S_FAILURE;
	return ret;
}